Abstract

We find that a microcylindrical axilens with a closed boundary and with an f-number less than 1 still can achieve the properties of long focal depth and high transverse resolution, unlike a microcylindrical axilens with an open boundary, which fails to maintain those properties for low f-numbers. The focusing characteristics of the closed-boundary axilens and the open-boundary axilens are numerically investigated based on the boundary integral method. The numerical results show that the ratio of the extended focal depth of the closed-boundary axilens to the focal depth of the conventional microlens can reach up to 1.26 and 2.12 for the preset focal depths 3 and 5 µm, respectively, even though the f-number is reduced to 1/3.

Figures (5)

(a) Variation of the axial intensity of a diffracted field with the axial distance around the focal region for the designed CBAs with different predesigned focal depths. Curves a and b correspond to the preset focal depths δf=3 and 5 µm, respectively, with f/#=1/2; curve c corresponds to δf=0, i.e., the conventional cylindrical lens. (b) Variation of the lateral distribution of the diffracted field intensity on the three observation planes, with f/#=1/2. The dashed curve corresponds to the observation plane at y=-7.25µm, the solid curve corresponds to the observation plane at y=-8.91µm, and the dotted–dashed curve corresponds to the observation plane at y=-10.84µm.

Intensity distributions of the electric fields plotted in a gray-level representation, corresponding to Fig. 2; (a) for δf=3µm, (b) for δf=5µm, and (c) for the conventional lens, i.e., δf=0µm. The bright (dark) regions indicate the areas of high (low) field intensity.